Grinding disk



April 93 H. w. H. BETH 2,078,120

GRINDING DI SK Filed March 27, 1933 Husa 14 H. 851 71 WITNESSES I (7M 6;Q? I H: 3% N1 Mm,

Patented Apr. 20, 1937 PATENT OFFICE GRINDING DISK Hugo W. H. Beth,Worcester, Mass, assignor to Norton Company, Worcester, Mass" atcorporation oi Massachusetts Application March 27,

4 Claims.

This invention relates to a bonded abrasive grinding disk, andespecially to a grinding disk which presents an extensive flat surface,for a grinding operation.

Heretofore, grinding disks adapted for grinding with their flat faceshave comprised solid abrasive bodies cemented or otherwise suitablysecured to a rotatable support, such as a rotatably mounted metalplate,whereby the entire flat wheel face may be employed for a grindingoperation. It has been found that grinding wheels of this type areunsatisfactory for many of the strenuous grinding operations to whichgrinding disks are commonly subjected. One of the many common uses for adisk type of grinding wheel is a dry grinding operation, wherein theleaf of a spring, such as commonly used in vehicles of today, is passedbetween two rapidly rotating disks so arranged that both of the opposed,substantially flat faces of the spring leaf are simultaneously ground. Adry grinding operation of this type rapidly brings the abrading surfaceof the grinding disk to an extremely high temperature. This high temperature on the operative wheel face is usually reached long before otherportions of the wheel or its supporting plate experience any appreciablechange in temperature due to the heat of grinding. As a consequence, theoperative face of the grinding wheel tends to expand at a very rapidrate, while the rest of the wheel and its supporting plate resist saidexpansion, thereby resulting in uneven internal wheel stresses whichusually result in wheel breakage, often spoiling the work andendangering the machine operator.

To overcome these difficulties, various devices, such as chucks, havebeen employed to clamp separate small abrasive blocks to a rigid supportso that their end faces could be moved in a fixed circular path andcooperate to produce a grinding operation. These chucks have proved tobe cumbersome, expensive devices, and the abrasive blocks are narrow sothat the total grinding surface presented thereby covers but a verysmall portion of the area bounded by the circular path 5 within whichthe blocks are rotated. Abrasive blocks commonly used in these chucksmust be carefully shaped, and in some cases they must be cemented toprecisely shaped clamping members so that they may be accurately seatedwithin 50 their respective chuck jaws, thereby resulting in an expensiveconstruction.

It is, therefore, the primary object of this invention to provide aninexpensive grinding disk construction comprising an abrasive body ofany de- 55 sired thickness having an extensive fiat operative 1933,Serial No. 662,857

face occupying the major portion of the area included within the wheelperiphery and wherein uneven expansions within the disk due to suddentemperature changes may be properly compensated for.

A still further object is to provide a simple arrangement whereby aplurality of individually fashioned abrasive sectors, or a unitarygrinding wheel having sectorportions, may be removably but rigidlysecured to a rotatable disk-shaped support.

A further object of this invention is to hold an expansible grindingdisk of sector formation, whether made as an integral body or as spacedunits, on a rigid disk-shaped supporting plate in such a manner thateven if fracture of the disk occurs between adjacent sectors, theabrasive body will be firmly secured in position, whereby every sectorwill be individually mounted and positively secured to the supportingplate.

With these and other objects in view, as will be apparent to one skilledin the art, this invention resides in the combination of parts set forthin the following description and appended claims.

In the drawing illustrating a grinding disk and support thereforembodying this invention:

Fig. 1 shows a plan view of thepreferred type of grinding disk ascovered by this invention;

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1;

Fig. 3 shows a modified construction of a grinding disk embodied in thisinvention;

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 shows a further modification of this invention; and

Fig. 6 is a detailed view of a preferred type of disk anchoring device.

In accordance with this invention, there has been provided a bondedabrasive grinding disk having a substantially flat grinding facearranged to expand without breakage or surface distortion when subjectedto localized surface heat caused by the friction of grinding. The diskis composed of bonded abrasive sectors, which may be formed as anintegral body or as spaced, individually manufactured segments, Thesesectors are of such size and shape, without reference to the definitionof the geometrical term sector, that they cooperate to provide anextensive flat grinding surface which covers the major portion of thearea bounded by the disk periphery. To provide for expansion of thegrinding surfaces, the operative face of the disk is cut by a series ofnarrow grooves which are preferably radial of the disk and are ofsufiicient depth and widthto permit the grinding face to expand underheat of grinding, without causing breakage'of the disk face. If the diskis composed of separate bonded abrasive sectors, they are secured to asuitable rigid support in sufficient spaced relation to compensate forsurface expansion of the disk grinding face. The spaces between theadjacent grinding sectors may be left open, or they may be partiallyfilled with a suitable cementitious medium which may allow for a slightexpansion of the surface portion of each abrasive sector and yet be ofsuflicient strength to hold the sectors together as an easilytransportable unit. The sectors are arranged as an annulus having asubstantially continuous grinding face, in which the spaces therebetweenare preferably only wide enough to permit of expansion and permit readyassembly. In some cases, the spaces may be wholly filled withcementitious material which permits lateral expansion of the individualsectors.

The back of each sector is provided with anchoring devices imbeddedtherein by suitable cement, such as Babbitt metal, sulphur or othermaterial. The sectors are removably secured to a rotatable support, suchas a rigid metal disk, by'clamping members passing therethrough andengaging the imbedded anchoring devices which take all of the rotativeand frictional thrust of grinding. Each sector is preferably held inplace by more than one clam-ping member, whereby the sector isdefinitely located and positively secured in position.

When the grinding disk comprises an integral unitary bonded abrasivebody, its fiat operative grinding face is cut by a plurality of narrowgrooves forming surface cutting sectors thereon. In this type ofgrinding disk, any breakage caused during the abradingoperation willnecessarily occur along the line of the grooves in the disk and cannotinterfere with the grinding operation, since the clamping members willstill serve to hold the sectors firmly secured as individual members totheir rotatable support. The grooves are preferably very narrow and ofsufflcient depth to permit lateral expansion of the sectors due to heatof grinding and yet provide a rigid grinding disk structure which may beeasily transported as a unit without any backing support.

The preferredembodiment of this invention, as illustrated in Figs. 1 and2 of the drawing, comprises a support Ill for a grinding disk which ismade of metal or other suitably rigid material of any required shape andsize. As illustrated, the support In is preferably a disk-shaped memberor plate having a central aperture ll adapted to slidably fit over a hubI2 on the end of a supporting shaft l4 which may be mounted for positiverotation in any convenient manner. A plurality of holes |5 are providedin spaced relation close to the aperture II and arranged to receivemounting screws l6 which pass through the plate l0 to positively secm-eit to the end of shaft l4 for rotation therewith.

. Thegrinding disk preferably comprises a plurality of abrasive sectors20 of suitably bonded abrasive material, and preferably grains ofalumina, or silicon carbide bonded by vitrified ceramic material,rubber, resinoids, sodium silicate, shellac or other suitable bonds, asare well known in the art. These sectors are of any desired size and areindividually and removably secured adjacent to the supporting face 2| oftheplate III in such a manner as to form an extensive, fiat,substantially continuous grinding surface 22. As illustrated, thesectors are preferably so shaped as to cooperate and provide an annulargrinding member having a relatively small central hole23, through whichaccess may be had to the screws l6 which serve to fasten the plate IIIto the rotatable shaft M. In order to provide a maximum size for thegrinding disk face, the central hole 23 is small in diameter. The screws6 and holes l5 passing through the plate ID are located as close to thehub l2 as practicable so that they may be accessible at all times formounting the grinding disk assembly. Each abrasive sector 20 may beconstructed as a separate article of manufacture independent of itssupport, and it is so made that it may be individually and removablyfastened to the plate It) by means of suitable clamping devices. Thepreferred type of clamping device, as illustrated, may comprise ananchoring member fastened to each sector and adjustably secured to thebacking disk Ill. The anchor members may comprise the nuts 24, each ofwhich is imbedded in a recess 26 in the rear face of a sector and ispositively and permanently secured thereto by any suitable material 21,such as a Babbitt metal, sulphur or other cementitious medium which mayserve to secure the nut integrally with the abrasive sector. I

As illustrated in Figs. 2'and 6, each nut 24 is provided with a reducedportion 29 terminating in a flat engaging surface 30 which lies slightlyabove the rear surface'3l of each sector when properly located andsecured within its recess so that the engaging faces 30 may locateagainst the face 2| of plate III to provide a positive sector mountingsurface and hold the sector faces parallel with the disk. The nuts 24are each secured within their respective recesses 26 with the reducedportions 29 near the rear faces of the sectors so that the cementitiousmedium 21 may engage each of said reduced surfaces with ,a wedgingaction to firmly hold the nuts 24 in their respectively correctpositions integral with the sectors. Hence, any force tending to pullthe nuts from the sectors will result in wedging them more securely intheir respective recesses. The plate I0 is further provided with aseries of holes 33 passing therethrough at predetermined locations andarranged to receive screws 34 therein, each of which has a threadedportion arranged to engage one of the nuts 24 and thereby tightly clampeach sector in correct operative position relative to the plate Ill andthe other sectors. It will be appreciated that the screws 34 will pullthe nuts 24 towards the plate l0 until the nut faces 30 engage the face2| of plate l0 and thereby serve to positively locate the sectors 20.Since the nuts project slightly from the rear faces of the sectors,there will be no tendency for the clamping screws to pull the nutsawayfrom the sectors, and a positive sector support will be assured.

If desired, a soft, compressible paper pad 35, commonly known in the artby the term wheel blotter, may be inserted between the sectors and theface 2| of the plate I to further aid in supporting the sector wheelupon its back plate I0. If a wheel blotter is used, holes are cuttherethrough so that the nuts 24 will have their respective surfaces 30positively engage the face 2|--of supporting plate Ill andcooperatewiththe screws 34 tdprovi'de positive locating devices for the abrasivesectors.

These sectors are preferably so' shaped and the locating devices 24 are'so positioned that the assembled sectors are mounted in spaced relationrelative to each other. This spacing between the adjacent sectors ispreferably small, but it must be sufiicient to provide for expansion ofthe individual sectors due to the heat of grinding and it must besufiicient to permit replacement of the individual sectors when desired.For example, one type .of sector grinding disk especially adapted fordry grinding the flat faces of large springs wherein an excessive heatof grinding is quickly developed is 20 inches in diameter, 2 inchesthick and has six sectors which are spaced only 3 of an inch apart. Itwill be clear to one skilled in the grinding art that these dimensionsmay be varied, depending upon the type of work to beground.

A modification of this invention embodies a grinding disk construction,as illustrated in Figs. 3 and 4, wherein a plurality of bonded abrasivesectors Ml similar in form to the sectors 20 may be secured together inpredetermined spaced relation around a central hole 44 to form anannular shaped grinding disk which may be easily transported as aunitary member independently of any supporting plate and yet is soconstructed that it may allow for expansion of the individual sectorsclue to heat of grinding without breakage of the sectors. To accomplishthis, the opposed faces M of each of the adjacent sectors are securedtogether by any suitable cementitious medium 42 which may allow forslight expansion of the adjacent abrasive sectors'due to heat ofgrinding and yet be of sufiicient strength to hold the sectors togetheras an easily transportable annular unit. Such a cement may be composedof glycerin and litharge. or sulphur, or sulphur and finely divided cokeof a composition known as lavasul, or a resinoid such as a reactionproduct of phenol and formaldehyde or their homologues. This cement 32may completely fill the interstices between the opposed faces ofadjacent sectors, or it may only partially fill the spaces between theadjacent sectors, as shown in Fig. 4, so that the upper or face portionsof the adjacent sectors will be free to expand as required by thetemperature gradient between the cold backing and the heated grindingface.

One type of integral sector grinding diskwhich may be employed in a drygrinding operation, wherein the operative grinding face of the disk issubjected to sudden changes in temperature due to the friction ofgrinding, comprises a grinding disk having six sectors forming an.annulus 20 inches in diameter and 2 inches thick. These sectors arespaced approximately 1; of an inch apart and the cemen titious me diumtherebetween fills the lower half of the space, leaving a groove or airspace between the adjacent opposed sector faces 4! which is about 1%inches deep.

To prevent collapse of the grinding disk during shipment,thecementitious medium completely fills the space between the adjacentsector faces M close to the periphery of the grinding annulus. Thiscementitious portion 33 need not extend radially inwardly very far, andin the instance of the wheel cited, extends from the wheel peripherytoward the wheel center for approximately one inch.

To further strengthen the annular unit, both during shipment and in use,the periphery may be wound with several turns at a tough resilient wireunder sufficient tension to resist the centrifugal force of diskrotation, and the adjacent turns of wire may be. suitably securedtogether at various positions, as by a solder or other means.

.engages the periphery of the assembled disk unit.

The wire'is wound around the disk under resilient tension, the amount ofwhich depends upon the size of the disk and the centrifugal force towhich the unit will be subjected. The cement 42 located between thesector unit 40 fills a suiiicient portion of each crevice between thesector spaces 4| so as to hold the sectors in fixed spaced relationagainst the inward pressure of the resilient tensioned wire. In thismanner, the major portion of the centrifugal force set up by rotatingthe grinding disk is received by the resilient wire and not by theanchoring devices or nuts 24 embedded within the sectors and thecooperating screw bolts 35. Without the wire engaging the periphery ofthe disk, centrifugal force might tend to tear the embedded nuts 24loose from the sectors, it being observed that these embedded nuts arenear the inner faces of the sectors and that the center of gravity ofthe individual sector lies in a plane outside of the anchoring devices.

The assembled annulus is removably secured to I a rotatable metal plate41 in the same manner as disclosed in my preferred constructionillustrated in Figs. 1 and 2 and described heretofore.

It will be appreciated that a construction of this type permits thesectors of the grinding disk to expand individually towards each other,and the upperportion of each sector close to and within the grindingzone may be free to expand at a different rate from that of the backingplate without causing internal stresses within the sectors which, in thecase of a solid grinding disk, have usually caused breakage.

. A further modification of this invention embodies the use of a unitaryor integral abrasive disk 5% (Fig. 5) having an extensive, substantiallyfiat grinding face 55 divided by a plurality of grooves 52. This disk ismade in one piece by the standard methods of bonding abrasive grains, inwhich the bond may be vitrified ceramic material, rubber, resinoid, etc.The grooves 52 are preferably arranged to run radially oi the disk, andthey are of sufficient width and depth I to permit the varioussector-shaped portions of the cutting face to expand under heat changesin the surface of the disk caused by the friction of grinding withoutresulting in fractures of the grinding disk through its operative face.For an ordinary dry grinding operation, the disk may be approximately 20inches in diameter, 2 inches thick and separated by grooves 1 inch deepand it; of'an inch wide in to six or more sectors. The grooves in aunitary grinding disk of this type serve to separate the disk body intospaced sectors which may individually expand and contract. As shown inFig. 5, these sectors have their clamping'devices so located that theyare individually secured to the supporting plate 55. If, through abuse,excessive stresses cause breakage of the grinding disk, it will occuralong the weakened sections below the rooves. However, such breakage ofthe disk will be immaterial, since the sectors are individually andrigidly secured in place. When the sectors are individually fashionedbefore mounting, as shown in the preferred type of this invention, thisconstruction simply amounts to a pre-breakage of the disk sectors alongsections where the grooves exist in the integral wheel structure. Itwill be appreciated that it is preferable to make the 5 grooves 52 asdeep as practicable and still have the grinding disk strong enough forshipment as a unit without other support. A grinding disk of this typemay be removably secured to a rigid,

rotatable supporting plate 55 in the same manner as disclosed in thepreferred construction illustrated in Figs. 1 and 2.

It is to be understood that the term disk shaped support as used in theclaims is intended to cover any construction such as spiders orequivalent supports, wherein clamping members may be rigidly supportedin correct positions to engage anchoring devices within the grindingdisk.

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is:

1. A grinding disk comprising a plurality of bonded abrasive sectorsspaced apart by open grooves and arranged to provide an extensive fiatgrinding surface which is free to expand under heat of grinding, ananchoring device embedded within the lower portion of each sector andhaving a portion projecting therefrom, a rotatable disk shaped supportengageable only with the anchoring devices, and separate clampingmembers removably and rigidly fastening the anchoring devices to thesupport at various predetermined positions and serving as the sole meansto position the segments relative to each other and in predeterminedspaced relation to the support. 2. A grinding device comprising arotatable disk shaped support, a plurality of separate spaced sectors ofbonded abrasive material thereon which are arranged to provide anextensive flat grinding surface, a cementitious medium -partialiyfilling the lower portions of the spaces between and uniting theadjacent sectors to form an-integral annular grinding structure which istransportable as a unit independently of its rotatable support, theupper portions of the spaces between the adjacent sectors being leftopen to provide for the individual expansion ofthe face portions of eachsector when subjected to temperature changes due to the friction ofgrinding, anchoring devices imbedded within the sectors, clampingmembers engageable with the rotatable support which removably andrigidly engage the anchoring devices and serve as the sole means tolocate and transmit rotation to the sectors and position them withrespect to the rotatable support.

3. A grinding device comprising a rotatable I disk shaped support, abonded unitary abrasive grinding disk having an extensive flat grindingface including the major portion of the area within its periphery, saidface being provided with a plurality of relatively narrow groovesextending substantially radially of the disk, which serve to separatethe disk into closely adjacent integrally united grinding sectors, andwhich provide for expansion of the grinding portions of the sectors.anchoring devices imbedded within and proiecu ing laterally from therear face of the abrasive disk, and clamping members engageable with therotatable support secured to the anchoring devices, said clampingmembers and anchoring devices serving as the sole means to secure theabrasive disk to its rotatable support in spaced relation therefrom.

4. A grinding device comprising a disk shaped rotatable support, aplurality of bonded abrasive sectors arranged in spaced relation thereonto provide an abrasive. annulus having a cylindrical periphery and afiat grinding surface, anchoring devices embedded within and cemented toeach sector, clamping members engaging the anchoring devices andremovably and individually securing the sectors to the rotatablesupport, a resilient wire wound around and secured in position againstthe peripheral surface of the disk under a tension sufficient to resistthe centrifugal forces set up during normal rotation of the grindingdevice but to permit expansion of the sectors due to heat of grinding,and a cementitious medium partially filling each crevice betweenadjacent sectors to resist the pressure of the tensioned-wire butmaintain the operative grinding faces of the sectors separated bygrooves sufficient to provide for expansions thereof caused by the heatof grinding.

HUGO W. H. BETH.

